1. Field of the Invention
The present invention relates to sensing and locating the occurrence of acoustic events. More specifically, the present invention relates to using a two-dimensional array of sound sensors to detect and generate positional information of acoustic events in three dimensions.
2. Description of the Related Art
Determining the three dimensional location of acoustic events in a space using a two-dimensional array of sound sensors presents a variety of challenges. However, successful and accurate implementation would be of considerable usefulness. Some applications may include security surveillance, equipment monitoring, research, etc. One practical application for the present invention is in the field of military weapon firing exercises; in this example, the event is often the detonation or impact of ordnance. Commonly, in waterborne environments, such arrays may take the form of hydrophones located on buoys. The location of a detonation within a training range or buoy field can be used to determine the accuracy of the firing unit. Inherent in any such system will be error in measurement and calculation. Some detonations may occur at elevations above or below the water's surface—outside of the plane of the array. Further, the near simultaneous detonation or occurrence of acoustic events may complicate differentiation of those events.
While the notion of using an array of sound sensors to create such a training range is known, the above described complications produce inaccuracies that reduce effectiveness. The ability to account for these issues is required to make an array or training range more effective, particularly when multiple units are participating (e.g., ships, aircraft, or land based artillery). Error in position information or sound detection may introduce inaccuracies into such systems, regardless of how accurate the sensors and other components might be.
Most array detection methods do not address the effect or complications arising from out of plane events. Some virtual systems estimate the trajectory of the ordnance based on a known firing location and an estimated two dimensional or planar equivalent to the strike location. In general, these systems focus on the plane of the array, as if all acoustic events occurred at the same elevation as the array, which can limit usefulness to certain types of ordnance or certain types of surface units. Further, such systems are limited in their ability to support the training or simulation of air and undersea assets.
The complications of near-simultaneous acoustic events have prompted two general approaches. In exercises where multiple units fire into the same space or range, some prior technologies delay the rate of firing in order to separate the performance of the various units, and to permit allocation of a detonation to a particular unit. Of course, this assumes that such a delay in firing does not reduce the efficacy of the training, the exercise performance, or ultimately the performance in combat.
The U.S. Department of Defense Live Fire Testing and Training Program uses an array of sound sensors to detect ordnance striking water, called the Integrated Maritime Portable Acoustic Scoring and Simulator (IMPASS). This system is directed to detection of events at the two dimensional plane of the water's surface. Further, the IMPASS acoustic scoring buoy system disables the detection circuit for a predetermined time after a first sound impulse is detected, rendering it impossible to score near-simultaneous detonations in the buoy array. The time delay before a subsequent sound impulse can be detected is predetermined (e.g., a three second delay). Unfortunately, this delay interferes with the ability to detect multiple near-simultaneous detonations in the same buoy array. IMPASS does not sort multiple sound waves or impulses that arrive closely spaced in time at a given buoy's location within the buoy array, which is needed in order to assign a given sound impulse to a specific event. The first sound impulse that arrives at one sensor within an array could be the sound impulse generated from a second event, depending on the sensor location within the array geometry.
Another example of a sensor array within a buoy system is provided by Pub. No. US 2003/0152892 to Paul C. Huang, et al. This approach uses a parallel virtual three dimensional graphical target range (e.g., virtual coastlines) formed from known geographic data along with data from the fire control or weapon system of a participating naval platform. A spotter subsystem links the sensors in the buoy system to the naval weapon system. Additional information may be collected from video or radar monitoring of the range. This approach is directed to detecting an acoustic event in two dimensions for the purpose of calculating an estimate of the trajectory of the ordnance, which is then used in creating a three dimensional graphic display; any error in positioning or in the speed of sound is assumed to be minimal. This use of a buoy array is not directed to the detection of out of plane events, near simultaneous events, or the minimization of error.